A first known immersed turbo-generator set of this type comprises:
an elongate housing having a longitudinal axis, and immersed in a duct through which water flows;
a turbine mounted in the rear portion of the housing on a shaft that runs along the axis of the housing, the turbine blades projecting radially from the housing to be rotated by the flow of water;
a gear box disposed in an intermediate portion of the housing, the gear box being driven by the turbine shaft and driving an alternator shaft at a higher speed than the turbine shaft, the alternator shaft extending forwardly;
an alternator rotor mounted on said alternator shaft in a front portion of said housing;
an alternator exciter mounted on the alternator shaft to provide excitation current to the rotor; and
an alternator stator surrounding the rotor and including windings, a magnetic circuit and a supporting casing which surrounds the magnetic circuit and is in contact therewith.
The stator casing also constitutes a portion of the housing to dump a portion of the heat generated in the magnetic circuit directly into the water. The alternator is also provided with a gas cooling circuit.
A second immersed turbo-generator is similar, but does not have a gear box. It has a gas cooling circuit having tubes that are on the outside of the housing in order to cool the gas by means of the water flowing along the duct. Each tube is connected to the housing via two orifices, one at each end of the tube.
The front end orifices are arranged in a staggered configuration occupying two different transverse drilling planes in front of the alternator stator, the longitudinal distance separating said transverse drilling planes being at least equal to the diameter of the orifices to avoid exessively weakening the mechanical strength of the housing in the vicinity of said drilling planes. The rear end orifices are arranged in the same manner as the front end orifices, i.e. in two different planes.
Both generator sets are provided with an access tube running from the housing to the outside wall of the duct to give a way into the housing from outside the duct.
In the first generator set, said access tube leads to the intermediate portion of the housing where the gear box is located.
Both of these known generator set suffer from the drawback of great length which leads to high civil engineering costs to build a suitable water duct to house them. Further, where there is a gear box, access to the inside of the housing is made difficult because of the small amount of radial space left free around the gear box. Finally the front and the intermediate portions of the housings are interconnected by a flanges that project inwardly, hindering access to the electrical connections behind the alternator stator.
Preferred embodiments of the present invention provide a high power turbo-generator set with a gear box, but of reduced overall length, and with eased access to the housing for maintenance of the alternator. Mechanical strength of the housing is not jeopardized.